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6050H
User's Guide
Heater
The power to the bath heater is precisely controlled by the temperature controller
to maintain a constant bath temperature. Power is controlled by periodically
switching the heater on for a certain amount of time using a solid-state relay.
The front panel red/green control indicator (see Figure 3) shows the state of the
heater. The control indicator glows red when the heater is on and glows green
when the heater is off. The indicator will pulse constantly when the bath is
maintaining a stable temperature.
The heater has two power level settings. The "MED" and "HIGH" heater power
settings are used to more quickly heat the bath fluid up to the desired operating
temperature. These heater power settings may also be required for control at
higher temperatures. The "HIGH" setting is used to heat solid salt. The "LOW"
setting is used when controlling at lower temperatures, and for scanning at
slower rates. When controlling at the "MED" or "HIGH" heater power settings
instead of "LOW" the proportional band may need to be increased (typically two
or four times) to compensate for the increase in power gain. Otherwise the
temperature may oscillate.
Fluid Drain
The drain at the back of the bath (see Figure 5) is for factory use only. During
operation of the bath the drain plug must be screwed on tightly.
Temperature Controller
The bath temperature is controlled by Fluke Calibration's unique hybrid
digital/analog temperature controller (see Figure 3). The controller offers the tight
control stability of an analog temperature controller as well as the flexibility and
programmability of a digital controller.
The bath temperature is monitored with a platinum resistance sensor in the
control probe. The signal is electronically compared with the programmable
reference signal, amplified, and then fed to a pulse-width modulator circuit which
controls the amount of power applied to the bath heater.
The bath is operable within the temperature range given in the specifications. For
protection against solid-state relay failure or other circuit failure, the
microcontroller automatically turns off the heater with a second mechanical relay
anytime the bath temperature is more than a certain amount above the set-point
temperature. As a second protection device, the controller is also equipped with
a separate thermocouple temperature monitoring circuit which shuts off the
heater if the temperature exceeds the cut-out set-point.
The controller allows the operator to set the bath temperature with high
resolution, set the cut-out, adjust the proportional band, monitor the heater output
power, and program the controller configuration and calibration parameters.
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